The rectum is the end part of the large intestine that connects the colon to the anus. It is the area where a person holds stool before excreting it from the body. It is around 12–15cm in length.

The rectum, or intestinum rectum, forms part of the digestive system, sitting in the furthest area of the large intestine. It links the gastrointestinal (GI) tract to the anus. It comes after the last section of the colon, called the sigmoid colon, and is where the body stores feces before elimination.

In this article, we will discuss the function and anatomy of the rectum, as well as common conditions that may affect it.

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The National Cancer Institute defines the rectum as the final section of the large intestine closest to the anus. The total length of the large intestine is roughly 5 feet, with the rectum accounting for around 12–15 centimeters of this length.

After completing the process of digestion, the intestines use the muscular walls of the sigmoid colon to push feces into the rectum. The body stores feces in the rectum until defecation occurs. Stretch receptors in the wall of the rectum detect when it is full and stimulate the urge to excrete stool through the anus.

The large intestine contains four distinct parts:

  • Cecum: Also known as the ileocecal junction, this section joins the small and large intestines. The cecum helps absorb water and any remaining salts during the digestion process.
  • Colon: The colon is the longest portion of the large intestine. It also absorbs water and electrolytes.
  • Rectum: The rectum stores feces until a person is ready to have a bowel movement.
  • Anal canal: The anus is the final portion of the large intestine. It helps a person have bowel movements.

The position of the rectum is between the sigmoid section of the colon and the anal canal. The rectum contains two major flexures, or bends, known as the sacral and anorectal flexures. Additionally, there are three lateral flexures, known as the valves of Houston. These bends help support the weight of feces and help prevent a strong and immediate urge to defecate.

At the end of the rectum is a section called the rectal ampulla, which connects to the anal canal. The role of the ampulla is to act as a temporary storehouse for feces before its release via the anal canal. When the ampulla becomes full, the intrarectal pressure causes the anal canal walls to dilate and expand, allowing feces to enter the anal canal.

Some conditions that can affect the rectum include:

Hemorrhoids

Hemorrhoids are swollen veins that bulge in the rectum and anus. They do not always cause symptoms, but when they do, people may experience:

  • bleeding during defecation
  • protrusion of skin during bowel movements
  • discomfort, irritation, or itching in the anal area
  • pain in the anal area
  • sensitive lumps

Infections

Different types of infection can affect the rectum and often result in uncomfortable symptoms, such as itching, pain, and proctitis.

For example, a person may acquire a sexually transmitted infection (STI) after engaging in anal sex. This can include:

Sometimes, using antibiotics can lead to a bacterial infection of the rectum. This is because antibiotics can kill the beneficial bacteria that keep harmful types, such as Clostridioides difficile, away. The harmful bacteria can then overgrow and infect the rectum.

Fungal infections can also affect the rectum and rectal tissues. Examples of fungal diseases include:

Parasites can enter the body and cause harm, particularly when there is poor sanitation. The two main causes of parasitic infection in the intestine are protozoa, which are single-celled organisms, and helminths, which are worms. Parasites can cause a range of conditions that affect different components of the intestine, including the rectum.

Anal abscess

An anal abscess is a collection of pus in the tissue surrounding the anus or rectum. One typically occurs following an infection or blockage. A perirectal abscess occurs in the rectal region, and evidence suggests it may affect around 68,000–96,000 people in the United States each year. Treatment typically involves a doctor cutting and draining the pus-filled cavity.

Prolapse

Rectal prolapse is a condition where part or all of the rectal wall falls through the anal sphincter, which is the seal that contains the rectal contents. This condition is typically due to a weakening of the muscles that support the rectum.

There are three types of rectal prolapse:

  • External: Also known as full-thickness or complete prolapse, the entire wall of the rectum protrudes out of the anus.
  • Mucosal: Only the mucosa, or lining of the anus, sticks out through the anus.
  • Internal: Also known as an incomplete prolapse, the rectum folds in on itself but does not protrude out through the anus.

Incontinence

As the rectum stores feces, it plays an important role in controlling defecation as well as maintaining continence. So if a person experiences muscle injury, nerve damage, prolapse, or scarring of the rectum, it may mean the rectum is unable to function correctly, which can cause stool to leak through the anus.

Rectal cancer

is a condition where cancer cells form in the tissues of the rectum. There are not always symptoms, but rectal cancer can cause:

  • pain
  • changes in bowel habits
  • bright red blood in stool
  • leaks of diarrhea
  • constipation

Together, colon and rectal cancers are the second highest cause of cancer mortality in the U.S. Treatment options may include surgery, radiation therapy, chemotherapy, targeted therapy, and immunotherapy.

To help maintain rectal health and prevent rectal conditions, people can try to practice good anal hygiene. This can include regular bowel movements and practicing safer sex. Additionally, lifestyle changes can help improve rectal health and reduce the risk of rectal cancer. These can include:

  • maintaining a nutritious, balanced diet
  • avoiding smoking
  • avoiding alcohol
  • reaching or maintaining a moderate body weight
  • exercising regularly

It is advisable for a person to contact a doctor if they are experiencing rectal discomfort or any symptoms that may indicate a problem around the anal area. Any rectal condition can reduce a person’s quality of life, and it is best to address the problem as soon as possible to avoid potential complications. If a person is over the age of 50 years, they may want to consider discussing regular screening for rectal cancer with their doctor.

The rectum is the last section of the large intestine, and it connects the colon to the anus. It is where the body stores stool before a person is ready to have a bowel movement.

A range of conditions can affect the rectal area. Any of these can reduce quality of life by causing pain, discomfort, and incontinence. If a person is experiencing rectal issues, they should contact a doctor for a diagnosis.